One of the people who came across my blog recently was asking about thinning a softwood plantation. I appreciate the interest and questions from readers so I thought it would be a good idea to tackle this subject. I will look at softwood plantation thinning in this blog but it will apply to natural stands and to hardwood stands to some degree as well. I will write about hardwood thinning in a future blog.
Thinning, as most people would guess, is one of the most necessary steps in forest management. It is an absolutely necessary step in creating the most valuable trees in a woodlot. Mother nature has a way of putting too many new seedlings in an area, especially following a harvest operation or some natural disaster that removes most of the older trees. As a woodlot owner you have choices of what to do with an open area in your woodlot. For today’s blog I am going to assume that you want to restock (plant) the area with trees that are appropriate for the area. This is exactly what we have done at Watts Tree Farm. However, as a forest manager, you must be open to new ideas and techniques. What I had done 25 years ago is not the same as I would do now and I am sure things will be a little different 25 years from now. So forest management is dynamic and ever-changing. One of the changes we have made is to have more than one species in a new plantation. As a woodlot owner your thoughts about your woodlot and your needs from the woodlot will also change.
When a plantation is established the seedlings are usually planted closer than is necessary for the final projected crop. Trees are often planted 1.5 to 2.5 meters (5 – 8 feet) apart. At maturity, the distance between trees could be as much as 6 – 8 meters (20 – 25 feet). The initial plantation spacing is made based on the location and species. Some plantations can make to harvest, without thinning, at this spacing but only if the final crop is to be lower valued fiber for fuel or pulp wood. However, at Watts Tree Farm we are all about higher value not hight volume. The close planting does have its advantages. If trees are planed too far apart and do not have trees near them then they will grow wide and have heavy branches. These heavy branches will create low valued “knotty” wood. The trees will tend to grow out sideways, filling the space given to them, rather than up. Taller, straighter trees will generally have more value for lumber. But if trees are left too close for too long they will slow down their diameter growth. The larger diameter of a good tree is one of the most important factors of what will makes good sawlogs and therefore higher value. So occasional thinning is necessary. The timing of thinning will depend on how quickly the trees are crowding each other. As trees crowd each other they are competing for space. All of the trees in the plantation may begin to lose live crown. It is the amount of live crown or living needles that feeds the tree and gives it its ability to maintain good growth. Softwood trees naturally lose their lower branches because of shading. As trees grow taller and compete with each other they create shade on the lower branches. Some species do not tolerate share well and there for lose their lower branches more quickly. Trees can also be manually pruned at a young age which can help the tree create high quality clear wood and in some cases it can help reduce the incidence of disease. This also looks like a good topic for future blog. Most softwood trees need between 1/3 and 1/2 of their total height to have live, green branches, to sustain good growth. Estimating the percent of live branches in relation to the tree height can be a very good indication of the need for thinning.
Many plantations will benefit from an early “cleaning” or “pre-commercial” thinning. This first thinning gives you a very good chance at removing the poorest quality trees. Trees that are damaged by insects, disease or some other factor can be removed. Trees that are falling behind in height should also be removed as they are showing signs of being a weaker tree. The tallest, dominant trees with good characteristics of the species should be kept. Remaining trees should be “released” on al least one side and preferably two. This open space, where an inferior tree was removed, will allow space for the branches of the released tree to fill in and maintain a good healthy crown. The removed trees are simple left on the ground to slowly decay and provide nutrients to the growing trees.
Later thinnings, as the trees get older, will provide a “commercial” or useable product. Thinning done at this age, before the trees are of suitable sawlog size, usually end up as part of my fire wood supply from my woodlot. Although these thinnings are called commercial they usually do not provide enough income to support the cost of harvesting and extracting the wood. It will be up to you to decide if the extra time and/or expense it takes to remove this smaller diameter wood is worth it. In plantations, some people opt for removing every third or fourth row. This allows for convenient removal trails and can be a very simple thinning strategy. Later thinnings will make use of these extraction trails for efficient removal of more commercially valuable logs.If you are serious about managing your woodlot, you will need to do some periodic thinning. Good trees need space to grow. Plantations of trees, just like vegetables in your garden, need some tender love and care so that they can reach their true potential.
Until next time, keep safe and well.
***Click on any photograph to get a large image***